geem
Well-known member
No problem with a Duogen. Its just behind the boat. No rotating rope.
Hydrogenerators
- Thread starter Koeketiene
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Slowboat35
Well-known member
Tried to delete this - can't see how
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Slowboat35
Well-known member
What an appallingly rude reply. Do you speak to people face to face like that?
It is also, as you yourself have proved with the graph, totally incorrect.
That rule of thumb is only well kown and well used because it works.
Your graph categorically verifies my rule of thumb's 18l/hr at 80Bhp. That's damn close to 4gals, wouldn't (mustn't?) you agree? In fact it's absolutely spot on! I'd say an apology is in order.
You said 3l/hr at 6Kts. That's virtually idle consumption and doesn't sound the least bit likely, you must admit. You cruise at idle or a gnat's above? Whats 80Hp for then?
3GPH seems much more to the point as one normally cruises a diesel engine at 70-80% power so unless you have 80Bhp in a canoe?
Have a nice day!
It is also, as you yourself have proved with the graph, totally incorrect.
That rule of thumb is only well kown and well used because it works.
Your graph categorically verifies my rule of thumb's 18l/hr at 80Bhp. That's damn close to 4gals, wouldn't (mustn't?) you agree? In fact it's absolutely spot on! I'd say an apology is in order.
You said 3l/hr at 6Kts. That's virtually idle consumption and doesn't sound the least bit likely, you must admit. You cruise at idle or a gnat's above? Whats 80Hp for then?
3GPH seems much more to the point as one normally cruises a diesel engine at 70-80% power so unless you have 80Bhp in a canoe?
Have a nice day!
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lw395
Well-known member
What nonsense.
You might cruise the engine at 80% revs, but the governor adjusts the fuel, and hence the power to whatever is required to hold that RPM.
Cruising a yacht under engine is often a small fraction of full power. That 80HP is a reflection of the need for a lot more power as you push the 'hull speed' soft limit, and a reserve for headwinds, waves, weed on the bottom etc etc.
Maybe take a look at the vicprop calculator for some estimates of the actual power needed for a boat to do a certain speed.
3.3litres an hour should be around 20HP at the shaft.
geem
Well-known member
How many people cruise at full revs? 6 kts is a pretty good cruising speed under engine. Tick over is 800 rpm. 1200 rpm is max torque of engine so spot on for economical cruising. 5 kts is a good speed to engine economically when doing an Atlantic crossing.
Why do you think anybody in their right mind cruises with a sailing boat engine at full revs?
I will say again, your rule of thumb is a waste of time when applying it to a sailing boat. Nobody apart from dragster runs flat out! How doesn a rule of thumb that assumes you run flat out apply to a sailing boat auxillary?
Just for the record my boat weighs 18t. 5hp per tonne seems pretty good for my boat. Its a well respected rule of thumb applied to sailing boat auxiliaries. Maybe you should move over to the motorboat forum
Slowboat35
Well-known member
I hardly know where to start!
Where did you get this bizarre obsession about running flat out - or that the rule of thumb somehow assumes it? How can a simple ratio considering onlt power, fuel use and time have any input from throttle positon? Don't you understand what a ratio is? Again, you don't trouble to read what others write before slagging them off any more than you seem able to apply simple logic so I'll leave it at that.
If you cruise your boat at almost idle power you are very, very unusual. The figures you quoted (3.5l/hr from a 86Hp engine) which was queried by others, not just me, is almost ecactly the figure you'd expect such an engine to cruise at in Gph, so it was a very natural suspicion that a gross error in units had been made, as doubtless many - most other readers did too!
You have helped prove the rule of thumb I quoted is highly accurate yet continue to rubbish it so clearly no rational discussion is possible there.
I nope I am never unfortunate enough to meet you on the water, though I expect you can't possibly be as unpleasant in reality as you are here.
Where did you get this bizarre obsession about running flat out - or that the rule of thumb somehow assumes it? How can a simple ratio considering onlt power, fuel use and time have any input from throttle positon? Don't you understand what a ratio is? Again, you don't trouble to read what others write before slagging them off any more than you seem able to apply simple logic so I'll leave it at that.
If you cruise your boat at almost idle power you are very, very unusual. The figures you quoted (3.5l/hr from a 86Hp engine) which was queried by others, not just me, is almost ecactly the figure you'd expect such an engine to cruise at in Gph, so it was a very natural suspicion that a gross error in units had been made, as doubtless many - most other readers did too!
You have helped prove the rule of thumb I quoted is highly accurate yet continue to rubbish it so clearly no rational discussion is possible there.
I nope I am never unfortunate enough to meet you on the water, though I expect you can't possibly be as unpleasant in reality as you are here.
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john_q
Active member
Perkins 4236M 72 HP - For what it is worth have had this engine since 1994 and 3 crossings these are our figures
800 rpm idle
1,000 rpm 4 knots 2.3 litres an hour
1,500 rpm 6 knots 4.4 litres an hour
800 rpm idle
1,000 rpm 4 knots 2.3 litres an hour
1,500 rpm 6 knots 4.4 litres an hour
Slowboat35
Well-known member
I wonder what you think is snonsense, you don't trouble to explain. That's pretty damn rude too. Is such offensiveness a requirement on this forum? It seems incredibly widespread.
Thanks for the patronising advice which ends with you once again proving pretty well the rule of thumb, 3.5 l/hr at 20hp which is pretty damn close to the estimated 4.5, isn't it???
So where's the nonsense I wonder?
geem
Well-known member
Dear Mr Angry. Your rule of thumb is wrong. If you care to study the graph I attached you will see that at 1200rpm and 3.3lph my boat uses 50hp. Not really running on tick over is it at 50hp? You will note other people providing you similar evidence to this effect. Rather than get angry why dont you learn from your error in how sailing auxiliary engines operate rather than assuming everybody is getting at you?
Slowboat35
Well-known member
Waste of time arguing with you. (You have an exceptionally bizarre idea of what angry is by the way. Very odd indeed!)
I suggest, though, that you use the graph you yourself provided that proves categorically the rule of thumb I quoted is extremely accurate as everyone else but you can see.
That alone deserves an apology.
You are reading the right graph for your rpm derived figures - er - aren't you?
The blue one?
But then if, as you've stated you think you're getting 50bhp at 1200RPM and 3.3l/hr you clearly are NOT! Woops! The red line is SFC (look it up) and is not RPM related on this depiction. It merely reads from right to left and vv.
Apart from which you clearly understand little about piston engine fuel consumption if you fondly imagine you can derive that much power from 3.3l of fuel per hr! As any simple gross error check would tell you.
One can only doubt the credibility of your figures when you say at such and such RPM and so many lph the engine "uses" 50hp. There's more than a little confusion going on in your head with numbers, ratios and units, isn't there?
An 18ton boat does 6Kts on 6 or 7hp?
My none too slippery 10 tonner manages 5,5Kt on 15/18hp in calm water so I can believe 40-50 for yours at 6kts though it seems a litle high unless it's a motorsailer or trawler hull. What I find hard to swallow is managing that speed on just 6 or 7hp in a boat that needs 80!
Still, you'll doubtless have the last word and best of luck to your crew. I fear for them with a skipper so stubbonly unwilling to acknowledge when he is so demonstrably proven so badly inaccurate and wrong. It's a dangerous profile for a skipper.
Remember, 1 gallon per 20bhp per hour.
.4lb/hp/hr is another formula - the result is the same to all intents and purposes.
Just read the graph, (Either line will tell the same story on this occasion)
QED
I suggest, though, that you use the graph you yourself provided that proves categorically the rule of thumb I quoted is extremely accurate as everyone else but you can see.
That alone deserves an apology.
You are reading the right graph for your rpm derived figures - er - aren't you?
The blue one?
But then if, as you've stated you think you're getting 50bhp at 1200RPM and 3.3l/hr you clearly are NOT! Woops! The red line is SFC (look it up) and is not RPM related on this depiction. It merely reads from right to left and vv.
Apart from which you clearly understand little about piston engine fuel consumption if you fondly imagine you can derive that much power from 3.3l of fuel per hr! As any simple gross error check would tell you.
One can only doubt the credibility of your figures when you say at such and such RPM and so many lph the engine "uses" 50hp. There's more than a little confusion going on in your head with numbers, ratios and units, isn't there?
An 18ton boat does 6Kts on 6 or 7hp?
My none too slippery 10 tonner manages 5,5Kt on 15/18hp in calm water so I can believe 40-50 for yours at 6kts though it seems a litle high unless it's a motorsailer or trawler hull. What I find hard to swallow is managing that speed on just 6 or 7hp in a boat that needs 80!
Still, you'll doubtless have the last word and best of luck to your crew. I fear for them with a skipper so stubbonly unwilling to acknowledge when he is so demonstrably proven so badly inaccurate and wrong. It's a dangerous profile for a skipper.
Remember, 1 gallon per 20bhp per hour.
.4lb/hp/hr is another formula - the result is the same to all intents and purposes.
Just read the graph, (Either line will tell the same story on this occasion)
QED
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Slowboat35
Well-known member
As expected at 1500RPM using the rule of thumb.
geem
Well-known member
I dont know where to start! How many times do I have to tell you? Do you think I cant tell how much fuel I use? We have just crossed the Atlantic from Grenada to Horta. We log our hours. We can read our boat speed off the log and gps. We read our engines hours off the engine hour meter. If we believed your figures we would have run out of fuel halve way across the Atlantic! Instead I dip the tank I guess what? Its half full! When will you get it in your head that you are wrong? Which bit of the above information do you not understand or not believe. We do 5kts at 1000rpm. We do 6kts at 1200 rpm. Three years ago we motored from Bonaire in the ABC islands to Grenada. It was about three days on the engine none stop at 1200rpm, 6 kts in no wind conditions. Fill tank and beginning, fulled tank at the end. Average was 3.3lph.
If you cant read the graph that shows this than what else can I do.
Your rule of thumb is WRONG.
If you cant read the graph that shows this than what else can I do.
Your rule of thumb is WRONG.
geem
Well-known member
Slowboat35
Well-known member
One can only muse and wonder how anyone can get into such a tangled state of confusion with a fuel consumption rule of thumb that agrees totally with all the evidence he himself has provided, and then continues to rubbish it as nonsense! This is now on a level with a flat-earth discussion.
One must also observe that you have neglected to explain how you derived a figure of 50Hp from a graph that didn't involve Hp when you were apparently quoting from a completely different graph!
Or how an engine 'uses' horsepower.
Might we be permitted an insight into this little gem of confusion?
My 4.5 ton Sadler did 6'5Kts on c12Hp (max 24) at 2l/hr
My current 10 ton yacht does 5.5Kts on 20Hp (max24) at 4l/hr
Yet you are claiming your 18 ton boat does 6 Kt on 7-8Hp (max 80!) at 3.3l/hr?
That is about as believeable as a Cadillac using less fuel on a run than a Fiesta. As anyone can see.
And you wonder why I am sceptical about your figures?
nice day!
One must also observe that you have neglected to explain how you derived a figure of 50Hp from a graph that didn't involve Hp when you were apparently quoting from a completely different graph!
Or how an engine 'uses' horsepower.
Might we be permitted an insight into this little gem of confusion?
My 4.5 ton Sadler did 6'5Kts on c12Hp (max 24) at 2l/hr
My current 10 ton yacht does 5.5Kts on 20Hp (max24) at 4l/hr
Yet you are claiming your 18 ton boat does 6 Kt on 7-8Hp (max 80!) at 3.3l/hr?
That is about as believeable as a Cadillac using less fuel on a run than a Fiesta. As anyone can see.
And you wonder why I am sceptical about your figures?
nice day!
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geem
Well-known member
this is getting tedious.One can only muse and wonder how anyone can get into such a tangled state of confusion with a fuel consumption rule of thumb that agrees totally with all the evidence he himself has provided, and then continues to rubbish it as nonsense! This is now on a level with a flat-earth discussion.
One must also observe that you have neglected to explain how you derived a figure of 50Hp from a graph that didn't involve Hp when you were apparently quoting from a completely different graph!
Or how an engine 'uses' horsepower.
Might we be permitted an insight into this little gem of confusion?
My 4.5 ton Sadler did 6'5Kts on c12Hp (max 24) at 2l/hr
My current 10 ton yacht does 5.5Kts on 20Hp (max24) at 4l/hr
Yet you are claiming your 18 ton boat does 6 Kt on 7-8Hp (max 80!) at 3.3l/hr?
That is about as believeable as a Cadillac using less fuel on a run than a Fiesta. As anyone can see.
And you wonder why I am sceptical about your figures?
I dont really care how inefficient your engine installations are. Just because you burn a load of fuel doesnt mean I do.
I have never claimed my engine does 6kts using 7hp. That is your statement based on your inability to read the two graphs I posted.
I keep telling you that at 1200rpm, the maximum torque output of my engine, the power output as read from the graphs is circa 50hp. Its plain to see on the first graph. Red power curve, not to be confused with blue fuel curve.
I provide evidence from my own fuel consumption figures that are spot on with Perkins Sabres own predictions and we are still having this stupid argument ffs.
Why can you not believe the figures? If you are so pigheaded why not phone Perkins Sabre or one of the Perkins dealers and ask them the question? For most people reading the curve would be enough to realise their mistakes but I guess you either cant read graphs or come from that breed of people who believe conspiracy theories and want to burn 5G towers. I have no other explanation!!
Beneteau381
Well-known member
Oh dear me, my 50 hp VP MD22 uses about 1.8 ltrs per hour doing 5-6 knots, 1800 ish revs, weight about 8 tons fully laden. Tested, like Geem by brimming the tank and recording the hours run from top up to top up on the trip from Wales to Portugal. Its a function of HP used and efficiency of engine. Need to check your figures again dear boy!One can only muse and wonder how anyone can get into such a tangled state of confusion with a fuel consumption rule of thumb that agrees totally with all the evidence he himself has provided, and then continues to rubbish it as nonsense! This is now on a level with a flat-earth discussion.
One must also observe that you have neglected to explain how you derived a figure of 50Hp from a graph that didn't involve Hp when you were apparently quoting from a completely different graph!
Or how an engine 'uses' horsepower.
Might we be permitted an insight into this little gem of confusion?
My 4.5 ton Sadler did 6'5Kts on c12Hp (max 24) at 2l/hr
My current 10 ton yacht does 5.5Kts on 20Hp (max24) at 4l/hr
Yet you are claiming your 18 ton boat does 6 Kt on 7-8Hp (max 80!) at 3.3l/hr?
That is about as believeable as a Cadillac using less fuel on a run than a Fiesta. As anyone can see.
And you wonder why I am sceptical about your figures?
Beneteau381
Well-known member
My VP MD22 has direct injection by the injectors, a much more efficient form of delivering fuel to be combusted. This system is used on your engine as well. When my engine was first developed by Perkins, in conjunction with BL, it was a complete surprise to the BL engineers to find out how fuel efficent the engine and car (Maestro and Montego) was. Over 50 to the gallon. This was attributed to the direct injection system. Indirect injection is much less efficient. Perhaps the Slowman is confusing his "rule of thumb" because of his misunderstanding of the fuel efficiencies of different engines?
